Thanks for reporting. Upstream is scheduled to release new versions in about a month or so, and the next Debian stable update date will show up at https://release.debian.org/ when it is planned. There will be no extra releases of MariaDB 1:10.3.3x in Debian 10 "Bullseye" than the next stable update in some months. Thus, there are no releases to do extra backports to at the moment.
Note that Debian as an open source project does not provide any warranties or guarantees about software. If you are running MariaDB in a commercial setting and you want to have a contract that guarantees you always have a good version, you should seek a contract with one of the commercial vendors of MariaDB.